Use of packet-switched connections for transmitting synchronous communications, such as voice calls, and data across telecommunications networks is increasing. Such packet-switched connections allow for greater speed and throughput than do circuit-switched connections, and also make packet-switched data from other networks, such as the Internet, more readily available. Voice over Long Term Evolution (VoLTE) is a widely-used standard for transmission of voice calls over packet-switched connections.
Many telecommunications networks, however, still utilize access networks that provide circuit-switched connections, such as Global System for Mobile Communications (GSM) networks or Universal Mobile Telecommunications System (UMTS) networks, due to the substantial infrastructure investment needed to expand packet-switched access networks. Such circuit-switched access networks can provide speed or quality comparable to, or, at times, better than, the speed or quality of packet-switched access networks for some types of data, including synchronous communications such as full-duplex voice communications. Moreover, some telecommunications networks can utilize packet-switched access networks without any underlying circuit-switched access network, such as deployments of packet-switched service using the 700 MHz band formerly occupied by analog television broadcasts.
Because packet-switched access networks and circuit-switched access networks are sometimes available in different areas or at different times, a communication session can use multiple types of networks, e.g., as a user moves while talking on a cellular telephone. Techniques have thus been developed for moving communication sessions from packet-switched access networks, e.g., the Long Term Evolution (LTE) access network, to circuit-switched access networks, e.g., the GSM or UMTS access network, while maintaining continuity of the communication session, such as a voice call. One technique for such “handover” of a communication session from a LTE access network to a circuit-switched access network involves the use of the single radio voice call continuity (SRVCC) standard produced by the Third Generation Partnership Project (3GPP). With SRVCC, an eNodeB of a LTE access network determines that a communication session handover should occur based on a measurement report received from user equipment. The eNodeB communicates this to a mobility management entity (MME), which makes a handover request of a mobile switching center (MSC) server of a circuit-switched access network that is available to the user equipment. The MSC server (MSS) then prepares the circuit-switched access network for the handover, and communicates with an Internet Protocol (IP) multimedia subsystem (IMS) of the telecommunications network, the IMS maintaining continuity for the communication session during the handover. The MSS then sends a handover response to the MME, and the MME instructs the user equipment to connect to the circuit-switched access network to continue the communication session. Handovers can occur at various times throughout a communication session.